Article record types are record types that define different types of articles in Lightning Knowledge, such as FAQs, How-Tos, Policies, etc. They determine which fields, page layouts, and actions are available for each article type. To import an external knowledge base to Lightning Knowledge using the Knowledge Importer, you need to create article record types before the import and have each article record type in a separate CSV file. The CSV file name must match the article record type name exactly. Verified References: [Import Articles into Lightning Knowledge]